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Aug. 11, 2010 -- Menstrual cramps may actually change the structure of women's brains, according to new research in the journal Pain.

Primary dysmenorrhea (PDM) -- menstrual pain in otherwise healthy women -- affects between 20% to 90% of adolescent girls, researchers say. It is marked by cramps in the lower abdomen that start with menstruation and can last up to 72 hours.

Researchers led byJen-Chuen Hsieh, MD, PhD, of the Institute of Brain Science at the National Yang-Ming University in Taipei, Taiwan, used magnetic resonance imaging scans to look at the brains of 32 women with a history of menstrual pain and 32 women with no history of menstrual pain. Scans were conducted when the women were pain-free, and the researchers used these images to help create maps of the gray matter of the brain. The brain's gray matter comprises the bulk of nerve cells or neurons within the brain.

There were changes in the volume of the brain's gray matter among women who experience painful menstrual cramps. Specifically, there were decreases of gray matter in areas of the brain involved in pain transmission and mood regulation and increases in areas of the brain that are involved in pain sensations and in regulating certain hormones, the study showed.

“Our results demonstrated that abnormal gray matter changes were present in PDM patients even in absence of pain," the study authors write. "This shows that not only sustained pain, but also cyclic occurring menstrual pain can result in longer-lasting central changes." The researchers cite previous studies that have found brain changes in people with chronic, persistent pain conditions.

Menstrual Pain and the Brain

Although the consequences of these changes are not known, "these results indicate that the adolescent brain is vulnerable to menstrual pain." The next step would be to conduct studies to see what role hormones play in these changes, and to determine whether or not the gray matter changes are reversible,” the researchers write.

"There are certain brain structural changes that occur with menstrual cramps," says Duke Han, PhD, assistant professor of neuropsychology at Rush University Medical Center in Chicago. "These changes could be related to pain, but there could be other contributing factors in addition to pain that are causing these structural changes." Hormonal changes and stress may play a role.

But if these results are validated, "targeting treatments toward the brain axis where there are changes may help better focus therapies for menstrual pain," he says.

"Hormonal changes sensitize the neurons to pain so you are apt to feel more pain given a stimulus such as cramps," says Edna Ma, MD, an anesthesiologist at St. John’s Health Center in Santa Monica, Calif.

"If these brain changes are related to the pain, and we can find a receptor, it would make sense to target it and minimize the menstrual pain, but if it is hormone-related then those changes may be unrelated to the pain," she says.

Put another way: "Yes, it is true that there is pain and yes, it is true that there are brain changes, but this may not be cause and effect," she tells WebMD